1. Field of the Invention
The present invention relates to a hybrid vehicle that can be run by the power from an electrically driven motor in addition to an engine and that has an electrical drive (EV) mode in which the hybrid vehicle runs only off of the power from the electrically driven motor, and a hybrid drive (HEV) mode, in which the hybrid vehicle runs off of the power from both the engine and the electrically driven motor. More specifically, the present invention relates to an engine start control system of the hybrid vehicle, wherein the mode switch from the EV mode to the HEV mode together with the starting of the engine is carried out in a state in which the mode switch has a minimum influence on the compressive reactive force when the engine is started.
2. Background Information
The hybrid vehicle described above is well known and is described in, for example, Japanese Laid Open Patent Application No. 2007-126082. For this hybrid vehicle, a first clutch that allows for a change in the torque transfer capacity is included between the engine and the electrically driven motor, and a second clutch that allows for a change in the torque transfer capacity is included between the electrically driven motor and the drive wheels. For this hybrid vehicle, it is possible to select the electrically driven drive (EV) mode by shutting down the engine to release the first clutch and, at the same time, to engage the second clutch, so that only the power from the electrically driven motor is in use; additionally, it is possible to select the hybrid drive (HEV) mode by engaging both the first clutch and the second clutch, so that the power from the engine and the electrically driven motor is used for driving the vehicle.
For the hybrid vehicle described above, switching the mode between the former EV mode and the latter HEV mode is necessary. In addition, for the mode switching, carrying out the engine start control via the torque capacity control of the first clutch and the second clutch is necessary. As far as the mode switch control is concerned, the Patent Document 1 proposed the following engine start control technology when the engine start control is carried out by making progress in the engagement of the first clutch when the mode switch is carried out from the EV mode to the HEV mode.
That is, when progress is being made in the engagement of the first clutch when the engine start described above is carried out, the torque capacity of the first clutch is the sum of the torque for increasing the engine rotational speed and the torque corresponding to the engine friction portion; as cranking is carried out by such torque, when the engine makes a complete ignition and is started, and the before/after differential rotational speed of the first clutch becomes 0, the torque capacity of the first clutch is at the maximum value, and the engagement is made completely.